The present invention relates generally to communication networks, and more particularly, to call admission control in wireless networks.
In recent years wireless networks have gained popularity and have been widely deployed. With fast deployment of wireless local area networks (WLANs), the ability of WLAN to support real time services while maintaining quality of service (QoS) requirements has become an important issue. In order to support a wide range of traffic on a wireless network, the infrastructure must be capable of supporting various quality of service (QoS) requirements, including call admission. Call admission control (CAC) plays a significant role in providing the desired quality of service in wireless networks. CAC limits the number of call connections into the network in order to reduce network congestion and call dropping. CAC operates to maximize the use of available bandwidth, either in calls accepted or traffic scheduled according to channel utilization, while minimizing a blocking probability for new calls and call drop probability for connected calls.
IEEE 802.11 covers the media access control (MAC) layer and physical layer specifications for WLANs. The physical properties of the wireless medium and 802.11 MAC protocols impose an upper boundary on the number of admissible wireless voice over IP (WVoIP) calls a wireless network (WLAN) can support (i.e., the call capacity). The call capacity depends on many factors, including, for example, channel conditions, background data traffic loads, and multi-BSS (basic service set) interference. Admission of even one more call than the call capacity can bring the WLAN from stable to unstable, causing a significant degradation of the voice quality of admitted calls. CAC must therefore be in place to ensure the quality of service.
The call capacity for a network varies with network conditions and configurations. Metrics for use in CAC decisions, therefore, need to adjust to changes in wireless medium conditions and network traffic conditions. Local channel conditions which need to be accounted for, include foreign interference (e.g., from microwave radios, Bluetooth radios, etc.) that may only affect one or two access points (APs) rather than an entire WLAN. Also, frequency reuse in the WLAN may reduce the number of calls per AP as several APs can share the RF channel and its capacity. The amount of channel overlap may be difficult to predict due to the wide variety of deployments and radio propagation conditions found therein.
The call capacity or equivalently the number of additional admissible calls, Na, given a certain number of admitted calls is a promising metric for a reliable CAC procedure. However, the call capacity and Na depend on many aspects of the network conditions, including, for example, the wireless channel conditions, background data traffic loads, and QoS capabilities of the WLAN. These dependencies are often numerically intangible and only WLAN simulations can provide an answer for a given network condition. In field deployments, the combinations of wireless network conditions are unlimited, making it unrealistic to use metrics predetermined by network simulations. In addition, network conditions for a WLAN often change with time, thus making evaluating the call capacity or Na even more challenging.
Many CAC schemes have been proposed. Many of these schemes use metrics such as delay, jitter, and packet loss rate. However, these metrics do not possess the desired properties discussed above, and do not provide an optimal call admission decision. Moreover, existing CAC metrics do not provide predictive measurements, which allow the CAC to predict the impact of the admission of new calls on a WLAN before it actually admits the call. Furthermore, conventional CAC schemes often make the implementation complex and lead to performance degradation.
There is, therefore, a need for a dynamic and predictive method and system for use in call admission control to evaluate the number of additional calls that can be admitted without degrading the voice quality of admitted calls.